**The** *Leishmania donovani* **SENP Protease Is Required for SUMO Processing but Not for Viability**

**Annika Bea 1,**† **, Constanze Kröber-Boncardo 1,**† **, Manpreet Sandhu 1,2, Christine Brinker <sup>1</sup> and Joachim Clos 1,\***


Received: 10 September 2020; Accepted: 10 October 2020; Published: 14 October 2020

**Abstract:** The protozoan parasite *Leishmania donovani* is part of an early eukaryotic branch and depends on post-transcriptionalmechanisms for gene expression regulation. This includes post-transcriptional protein modifications, such as protein phosphorylation. The presence of genes for protein SUMOylation, i.e., the covalent attachment of small ubiquitin-like modifier (SUMO) polypeptides, in the *Leishmania* genomes prompted us to investigate the importance of the sentrin-specific protease (SENP) and its putative client, SUMO, for the vitality and infectivity of *Leishmania donovani*. While SENP null mutants are viable with reduced vitality, viable SUMO null mutant lines could not be obtained. SUMO C-terminal processing is disrupted in SENP null mutants, preventing SUMO from covalent attachment to proteins and nuclear translocation. Infectivity *in vitro* is not affected by the loss of SENP-dependent SUMO processing. We conclude that SENP is required for SUMO processing, but that functions of unprocessed SUMO are critical for *Leishmania* viability.

**Keywords:** *Leishmania*; SENP; Ulp2; SUMO; CRISPR; protease
